Surface Mount International Conference Proceedings


Author: F. M. Hosking
Company: Sandia National Laboratories
Date Published: 9/10/1996   Conference: Surface Mount International

Abstract: The rapid advancement of interconnect technology has resulted in a more “engineered” approach to designing and fabricating printed wiring board (PWB) surface features. Recent research at Sandia National Laboratories has demonstrated the importance of surface roughness on solder flow. This paper describes how chemical etching was used to enhance the solderability of surfaces that were normally difficult to wet. The effects of circuit geometry, etch concentratio~ and etching time on solder flow are discussed. Surface roughness and solder flow data are presented. The results clearly demonstrate the importance of surface roughness on the solderability of fine PWB surface mount features. * KEYWORDS: Surface Roughness, Chemical Etching, Solder Flow potentially larger relative percentage of unwetted surface area can rm.dt. The thinning of solder coatings around convex points, particularly at the barrel opening of a PWB plated through hole (PTH), often results in limited solder flow onto the topside land. This phenomenon is commonly referred to as a “weak-knee” and can be observed during typical PWB fabrication and circuit assembly. Solder joints at the “weak-knee” are often poor and can consequently fail prematurely. Chemical etching was recently demonstrated as a solution to this solder flow problem by roughening the barrel edge and enhancing solder flow [10]. There are numerous chemical and mechanical methods,

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